Protein phosphorylation is now recognized as central to the fundamental processes of cellular signal transduction. Alterations in protein phosphorylation may therefore constitute either a physiological or pathological change in an in vivo system. Protein de-phosphorylation, mediated by phosphatases, is also central to certain signal transduction processes.
The two major classes of phosphatases are (a) protein serine/threonine phosphatases (PSTPases), which catalyze the dephosphorylation of serine and/or threonine residues on proteins or peptides; and (b) the protein tyrosine phosphatases (PTPases), which catalyze the dephosphorylation of tyrosine residues on proteins and/or peptides. A third class of phosphatases is the dual specificity phosphatases, or DSP's, which possess the ability to act both as PTPases and as PSTPases.
Among the PTPases there exist two important families, the intracellular PTPases, and the transmembrane PTPases. The intracellular PTPases include PTP1B, STEP, PTPD1, PTPD2, PTPMEG1, T-cell PTPase, PTPH1, FAP-1/BAS, PTP1D, and PTP1C. The transmembrane PTPases include LAR, CD45, PTPα, PTPβ, PTPδ, PTPε, PTPξ, PTPκ, PTPμ, PTPσ, HePTP, SAP-1, and PTP-U2. The dual-specificity phosphatases include KAP, cdc25, MAPK phosphatase, PAC-1, and rVH6.
The PTPases, especially PTP1B, are implicated in insulin insensitivity characteristic of type II diabetes (Kennedy, B. P.; Ramachandran, C. Biochem. Pharm. 2000, 60, 877-883). The PTPases, notably CD45 and HePTP, are also implicated in immune system function, and in particular T-cell function. Certain PTPases, notably TC-PTP, DEP-1, SAP-1, and CDC25, are also implicated in certain cancers. Certain PTPases, notably the bone PTPase OST-PTP, are implicated in osteoporosis. PTPases are implicated in mediating the actions of somatostatin on target cells, in particular the secretion of hormone and/or growth factor secretion.
Thus, there is a need for agents which inhibit the action of protein tyrosine phosphatases. Such agents may be useful for the treatment of glucose intolerance including Type I diabetes and Type II diabetes, immune dysfunction including AIDS, allergic diseases, inflammatory diseases, and autoimmunity such as psoriasis, infectious diseases, obesity, cancer, diseases involving the modulated synthesis of growth hormone or the modulated synthesis of growth factors or cytokines which affect the production of growth hormone, or Alzheimer's disease.